The present invention relates to a knee support or replacement apparatus comprising
at least one outer joint and one inner joint which are arranged each side of a vertical, antero-posterior plane and which each comprise at least one proximal member and at least one distal member articulated together, PA1 first connection means for connecting together the proximal members of the joints and second connection means for connecting together the distal members of the joints, the connection means effecting mutual positioning of the joints along a common axis, PA1 attaching means for fixing the proximal members to a femoral part of a lower member and the distal members to a tibial part of said lower member, PA1 and means of guiding the pieces articulated together, enabling relative flexion movement, antero-posterior rolling connected with sliding, rotation and/or varus movement between said femoral and tibial parts, the guide means providing the members of each of said joints with a movement different from that of each of the other joints, PA1 said guide means of each joint comprising at least one guide surface of predetermined curvature in an articulated member and at least one corresponding follower element on the other articulated member, these articulated members of each joint further exhibiting bearing surfaces of predetermined curvature which cooperate during said relative movement between the femoral and tibial parts. PA1 said bearing surfaces of the guide means of each joint exhibit mutually different complex curvatures by means of which they are in only partial contact, at at least three points, during movement between the femoral and tibial parts.
According to the invention, what is meant by knee support apparatus is a knee orthesis and what is meant by replacement apparatus is a knee prosthesis or endoprosthesis.
In the following, what should be understood by femoral and tibial parts of a lower member is not only the parts of an existing member but also rigid upper and/or lower members replacing this member.
Thus, the proximal member may conform to an upper rigid member fixed to the femur, or it may extend along the femur and be fixed there and the distal member may conform to a rigid lower member fixed to the tibia or it may extend therealong and be fixed there.
Also in the following, what should be understood by flexion and extension is a relative movement between the femoral and tibial parts of a member about a substantially horizontal axis passing through the knee approximately from left to right. What is to be understood by rotation is a relative movement between these parts about a vertical axis. What is to be understood by varus movement is a relative movement between these parts about a horizontal antero-posterior axis. Finally, what should be understood by sliding and antero-posterior rolling is a relative movement between the ends of the tibial and femoral parts in an antero-posterior plane.
The ortheses are orthopaedic apparatuses which enable movement and articulation of a deficient member of a handicapped person. Such apparatuses consist of two rigid parts connected together by a joint at the knee, on one side of the leg or on both sides. The whole may be fixed by bands or boxes which run along the thigh and the leg. Ortheses used for the lower members currently have two symmetrical joints at the knee, which joints allow them only a flexion movement and at best simultaneous antero-posterior displacement of the proximal part on the distal part (c.f. EP-A-0297766, U.S. Pat. No. 3,779,654). However, physiological movement of the knee is three-dimensional and these ortheses inevitably cause stress to the ligaments, which runs counter to medical or surgical treatment.
Moreover, there are known multiaxial ortheses provided with interacting slotted planar plates successively permitting rearwards sliding of the tibia with respect to the femur at the start of flexion and then rotation (WO-A-92/15264).
There also exists a polyaxial knee protector which is three-dimensional (c.f. Poli-Axial knee protector by Generation II Orthotics, Inc., Vancouver, Canada) and which comprises a joint for fitting on one side of the deficient knee. In this joint, two segments of a sphere interact, said segments having two slots forming arcs of a circle arranged about an axis in offset manner. In the first degrees of flexion the proximal member moves, and, when it has reached the end of the range of its slots, flexion continues over the slot of the second segment of a sphere, thus giving three-dimensional movement, but not physiological movement. In fact, the physiological movement of the knee exhibits, owing to a system of ligament links, movement consisting of antero-posterior rolling and of sliding connected with rotation and varus movement. The rotation and varus movement occur, according to the majority of medical studies, mainly at the beginning of flexion, which this known apparatus does not permit.
An orthesis is also known as described at the start (U.S. Pat. No. 5,107,824), in which the guide means are formed of slotted spherical shells interacting together. Given that the centre of the shells of the outer joint of this apparatus is situated at a different point from the centre of the shells of the inner joint, blockage of the apparatus inevitably occurs since the outer and inner shells are also connected together firmly by rigid bands around the thigh and the leg. Moreover, the spherical shape of the shells and their intimate support one on another prevents the obtaining of a movement with a complex trajectory permitting following of the physiological movement of the knee.
Prostheses are orthopaedic apparatuses which enable persons who have lost all or part of their leg to walk. These apparatuses surmounted by a socket allow the disabled person to lean on his stump and a joint, situated at the knee axis, permits flexion of the prosthesis. For femoral prostheses for full amputation or for knee disarticulation it is impossible to position the prosthetic joint at its physiological point. The prosthetic joint is positioned lower than the physiological knee axis, which renders walking uncomfortable and gives the seated position an unaesthetic appearance, the thigh part being abnormally longer than the tibia part.